The general apparatus within which the present invention is utilized is believed to be well known in the prior art to provide a dielectric belt arranged and supported in an endless tensioned loop, the belt being provided with an electrically conductive coating underneath the dielectric. The belt is continuously cleaned and electrically conditioned for re-use as it approaches a print head which modifies the charge thereon to form a latent image which is subsequently developed with a toner; the toned image is transferred to paper and fixed such as by application of heat at a fusing station.
In the prior art, Paschen ionization has been employed in electrographic printers and plotters utilizing treated paper wherein the paper is rendered conductive through, for example, the introduction of salts; the surface receiving the electrostatic charge is coated with a thin (few micron) layer of dielectric material. Additionally off-set systems have been reduced to practice employing conductive drums and belt structures which are dielelctrically coated.
The prior art paper systems have had limited application due to the cost of treated paper. The drum systems require precision alignment mechanisms to establish and maintain the necessary Paschen spacing over the full print width. Belt structures have been devised which employ textured surfaces to establish Paschen spacing but these surfaces are subject to wear and thus short life. Other spacing techniques have been deviced which employ abrupt discontinuities near the imaging region; these techniques suffer from contamination and abrasive wear.
The transfer of charge across an air gap has been described by Friedrich Paschen. In his experiments, Paschen discovered that the voltage necessary to initiate ionization was defined by a function that related the product of gas pressure and spacing of electrodes to voltage and determine that, at constant pressure, the voltage reduces to a function of distance only. Experiments have been conducted to establish the de-ionization potential and it is reported that ionization appears to extinquish at a level equal to or perhaps 20 volts below the Paschen function.
Clearly it is established in the prior art that air gap spacing is an exceedingly important consideration in electrographic printing.